Line spacing is correct, but don't let this distract you from how profoundly unsmooth the rendering is in the light theme version. The dark theme version is nearly identical though.

Those three operations should make the text rendering correct:
Disable hardware acceleration
Set gfx.canvas.azure.backends to direct2d1.1,cairo
Set gfx.content.azure.backends to direct2d1.1,cairo
https://renderingenginetest.netlify.com/
Dark theme can be tested by reversing the foreground and background colors in the HTML.
For reference, here is the correct GDI rendering of this website:
https://i.imgur.com/dWuZfbD.png
https://i.imgur.com/M4oKd7i.png
In Firefox ESR 52.4.1 (32-bit), text renders correctly:
https://i.imgur.com/InrXmeI.png
https://i.imgur.com/kn3bZra.png
which is the same as the GDI rendering of this website, except for some line spacing issues.
However, in Firefox 70.0b6 (32-bit), the rendering regressed and text no longer renders correctly:
https://i.imgur.com/Jn2NxGJ.png
https://i.imgur.com/qDxww7y.png
Line spacing is correct, but don't let this distract you from how profoundly unsmooth the rendering is in the light theme version. The dark theme version is nearly identical though.

Those three operations should make the text rendering correct:
Disable hardware acceleration
Set gfx.canvas.azure.backends to direct2d1.1,cairo
Set gfx.content.azure.backends to direct2d1.1,cairo

If you disabled HA, enumerating 'direct2d1.1' was redundant. You've been using cairo for text rendering.

Recently cairo code has been removed from the browser. See bug 1517077.

''PiotrGrochowski [[#question-1268750|said]]''
<blockquote>
Those three operations should make the text rendering correct:
Disable hardware acceleration
Set gfx.canvas.azure.backends to direct2d1.1,cairo
Set gfx.content.azure.backends to direct2d1.1,cairo
</blockquote>
If you disabled HA, enumerating 'direct2d1.1' was redundant. You've been using cairo for text rendering.
Recently cairo code has been removed from the browser. See [https://bugzilla.mozilla.org/show_bug.cgi?id=1517077 bug 1517077].

Question owner

What a facepalm it is that high quality text rendering has been removed. It is a regression. It is a dealbreaker because many if not most webpages have text in them so I'm not using the recent version.

What a facepalm it is that high quality text rendering has been removed. It is a regression. It is a dealbreaker because many if not most webpages have text in them so I'm not using the recent version.